Split-phase motor follow-up system



NOV. 26, 1946. sN cK 2,411,608

SPLIT-PHASE MOTOR FOLLOW-UP SYSTEM Filed May '1, 1943 =5 .1 5 70 ac. a usup/ 4) {y 1 4/ I 55.7 a? l g/ i 3nnentor fiber laiia'di' (IttomegUNITED STATES PATENT OFFICE SPLIT-PHASE MOTOR FOLLOW-UP SYSTEM RobertLesnick, Camden, N. J assignor to Radio Corporation of America, acorporation of Delaware Application May 1, 1943, Serial No. 485,301

3 Claims.

1 i This invention relates to the control of electric motors and moreparticularly to systems for controlling the speed and/or angulardisplacement of the rotor of an alternating current motor in 2 Electrondischarge tubes 29 and 3| are provided with their anode-to-cathodecircuits connected across the primaries of the transformers I5 and I1respectively. Resistors 33 and 35 are response to variations in theposition of a me- 5 provided in the cathode circuits of the tubes 29chanical input device. and. 3|. A voltage divider 31 is connected acrossAccurate control of the speed or angular disthe A.C. supply and isprovided with a variable placement of an electric motor is desirable intap 39 which is connected to the cathode circuit many applications; forexample, the control of of the tube 29 and through a resistor 4| to theguns, searchlights, directive radio antennas and control grid of thetube 3|. A second voltage the like. In displacement control systems itis divider 43 is connected across the A.C. supply usually desirable tocontrol the relatively large and is provided with a fixed tap 45 whichis conmechanical power output of a motor in response nected to thecathode circuit of the tube 3| and to a relatively small input such asmay be 0011- through a resistor 41 to the control grid of the venientlyproduced by a manually operable crank tube 29. or an indicator. Directcurrent motors are par- The operation of the above described systemticularly adapted to such applications as require is as follows: widevariation of.motor speed and motor torque. The A.C. supply voltagecauses currents to However, alternating current motors are less exflowthrough th motor windings 3 and 5, the pensive and alternating currentenergy is usually wifiiiirgsl and 9 of the transformer I5, as indimorereadily available than direct current. Thus, cated by the solid arrows,and the windings H for reasons of economy, it is frequently desirableand I3 of the transformer H, as indicated by to employ an A.C. motor,although the required the dash arrows. The impedances presented tocontrol circuits may be more complex than those the flow of current bythe windings and 9 and which would be required for aD.-C. motor. 5 IIand I3 are functions of the conductivities of It is the principal objectof this invention to the tubes 29 and 3| respectively. When the tubeprovide an improved method of and means for 29 is conductive and thetube 3| is cut off, current controlling the speed of a two phaseinduction flows through the paths indicated by the solid motor. arrows,causing the motor to rotate in one Another object is to provide animproved elec- 30 direction. When the tube 3| is conductive and tricalfollow-up system. the tube 29 is cut off, current flows through theThese and other objects will become apparent paths indicated by thedotted arrows, reversing to those skilled in the art upon considerationof the polarity of the winding 5 and causing the the followingdescription. with reference to the motor to run in the oppositedirection. The magaccompanying drawing, of which: nitude of the currentsthrough the motor wind- Figure 1 is a schematic circuit diagram of aings depends upon the impedances presented by system for controlling theenergization of an the secondary windings l and 9 or H and I3.alternating current motor, and V The variation in these impedances maybe ef- Figure 2 is a schematic circuit-diagram of an fected in either oftwo ways: If the transformers electrical follow-up system embodying theinl5 and H are designed so as to saturate as a stant invention. resultof the plate currents of the tubes 29 and Referring to Figure 1, a twophase induction 3|, the inductances of these secondary windings motor isprovided with phase windings 3 and are varied according to theconductivities of the 5. The phase windings are connected through tubes.If the transformers l5 and H are dethe secondary windings I, 9, H and HIof a pair signed so as not to saturate, the dynamic plate oftransformers l5 and IT to an A.C. supply, resistances of the tubes 29and 3| are reflected not shown. The secondary windings l, 9, H and inthe secondaries providing corresponding varia- |3 are connected in aWheatstone bridge circuit tions in secondary impedance. It will beaphaving conjugate pairs of terminals I9, 2|, 23 parent that both ofthese effects may be employed and 25. The motor winding 3 is connectedto together, if desired, by proper design of the the A.C. supply throughthe bridge by way of transformers l5 and H. In any event, the magtheterminals l9 and 2|. The motor winding 5 is nitude as well a thedirections of the currents connected across the bridge at the points 23and through the windings of the motor I are con- 25. A capacitor 21 isconnected across the motor trolled by variations in the conductivitiesof the winding 3. tubes 29 and 3|, thus providing control of the and 35provide automatic bias and may be adjusted so that both tubes aresubstantially nonconductive when the variable tap 39 is in its midposition.

When the tap 39 is moved away from its mid position, for example towardthe upper end of the voltage divider 37, the control grid of the tube 3|is provided with an A.-C. voltage which is in phase with the A.-C. platevoltage induced in the primary of the transformer 11. At the same timean equal voltage of opposite polarity is applied to the control grid ofthe tube 29. The impedances presented by the secondary windings H and I3are lower than those presented by the secondaries 1 and 9, causingcurrent to flow through the motor I, as indicated by the dash arrows.The magnitude of this current depends upon the distance the tap 39 ismoved away from the center of the voltage divider 31. Similarly themotor may be energized to rotate in the opposite direction by moving thetap 39 toward the lower end of the voltage divider 31. Thus therelatively small amount of energy required to operate the voltagedivider 31 will control the relatively large mechanical energy suppliedby the motor, both as to mag nitude and direction.

Figure 2 shows a follow-up system incorporating the motor controlcircuit of Figure 1. Similar parts of the circuits of Figures 1 and 2are. designated by corresponding reference numerals. A pair of synchrodevices 49 and 5| are connected in cascade between the A.-C. supply anda transformer 53. The secondary. of the transformer 53 is connectedbetween the control grids and the cathodes of the tubes 29 and SI. Therotor ofthe synchro transformer 49 is coupled to 4 as variable impedanceelements coupled to one of the motor windings through a Wheatstonebridge circuit and to the other of the motor windings as a seriesimpedance element. A typical application of this circuit in a follow-upsystem is described employing conventional synchro devices for derivingthe displacement control signals.

I claim as my invention: I

1. A control system including a motor including two phase windings, apair of electron discharge tubes, two transformers each provided asource of mechanical input, such as a manually I operable crank 55. Therotor of the synchro device 5! is mechanically connected, as indicatedby the line 51, to the rotor of the induction motor I.

Voltage from the A.-C. supply is transmitted through the synchro devices49 and El to the transformer 53. The amplitude of the voltage across theprimary of the transformer 53 and its polarity with respect to thepolarity of the supply voltage depends upon the relative positions ofthe rotors of the synchro devices 49 and 5|. The voltage induced in thesecondary of the transformer 53 controls the tubes 29 and 3H, causingthe motor to rotate in one direction or the other depending upon therelative positions of the rotors of the transformers 59 and 5!. R0-tation of the motor drives the rotor of the synchro device 5! toward anangular -position corresponding to that of the synchro device 69. Whenthe rotors of the synchro devices 49 and 5! are in positional agreement,the tubes 29 and 3! are equally conductive and the motor stops. If thecrank 55 is rotated to a new position the motor I will follow, drivingthe rotor of the synchro device '5! and any mechanical load which may beconnected thereto.

Thus the invention has been described as an improved control system fora two phase induction motor employing electron discharge tubes with aprimary winding connected between the anode and cathode of one of saidelectron discharge tubes and each provided with two secondary windings,all of said secondary windings being interconnected to ,form aWheatstone bridge circuit, means for applying A.-C. voltage to one ofthe phase windings of said motor through one pair of conjugate terminalsof said bridge circuit and applying said voltage to the other of thephase windings of said motor through another pair of conjugate terminalsof said bridge circuit whereby A.-C. voltages are presented between theanode and cathode of each of said electron discharge tubes, and meansfor applying oppositely variable A.-C. voltages between the controlgrids and cathodes of said electron discharge tubes.

2. A control system including a motor provided with two power inputwindings, a pair of electron discharge tubes, two transformers eachprovided with a primary winding connected between the anode and cathodeof one of said discharge tubes. and each provided with two secondarywindings, allot said secondary windings being connected together to forma Wheatstone bridge circuit, means for applying A.-C. voltage to one ofthe power input windings of said motor through one pair of conjugateterminals of said bridge circuit, means for applying said A.-C. voltageto the other power input winding of said motor through another pair ofconjugate terminals of said bridge circuit, and means for applying avariable A.-C. control voltage in opposite polarities to the controlgrids of said electron discharge tubes.

3. An electrical follow-up system including an output shaft which is tobe driven to a predetermined angular position, means for producing anA.-C. control voltage having magnitude and polarity related in apredetermined manner to the difference between said predeterminedangular position and the actual position of said output shaft, a motorprovided with two power input windings and coupled to said output shaft,two electron discharge tubes connected respectively to a pair oftransformers, each of said trans- .formers being provided with twosecondary windminals of said bridge circuit and to the other power inputwinding of said motor through another pair of conjugate terminals ofsaid bridge circuit, and means for applying said A.-C. control voltageto the control grids of said electron discharge tubes in oppositepolarities.

ROBERT LESNICK.

